The present invention relates to a motor in which a rotary shaft is supported by a yoke housing with bearings.
A typical motor includes a stator and a rotor accommodated in the stator. The stator includes a substantially cylindrical yoke housing with a bottom, and magnets. The magnets are arranged on the inner circumferential surface of the yoke housing along the circumferential direction. The rotor includes a rotary shaft, an armature and a commutator, which are fixed to the rotary shaft. The yoke housing has an opening at one end. The opening is covered with an end plate (base plate). The rotary shaft is supported by the yoke housing and the end plate with a pair of bearings.
In such a motor, it is preferable that the bearings be easily attached to the yoke housing and the end plate. For example, a document “JOURNAL OF NIPPONDENSO TECHNICAL DISCLOSURE” (Reference Number: 106-033, published on Jan. 15, 1996) discloses a resin end plate that has a structure for holding a bearing. This end plate has a holding portion on one side for receiving a bearing. A groove is formed on the circumferential surface of the bearing, and a projection is formed on an inner surface of the holding member that faces the outer circumferential surface of the bearing. When the bearing is fitted in the holding portion, the projection engaged with the groove so that the bearing is attached to the end plate while being prevented from moving in the axial direction. The end plate also includes a brush holder integrated with the end plate on a side opposite from the side on which the holding portion is formed.
To attach the bearing to the end plate while preventing the bearing from chattering, the holding portion needs to have high dimensional accuracy. However, since the end plate is made of resin, sufficient dimensional accuracy cannot be guaranteed by simply molding the end plate. That is, after molding, the end plate needs to be subjected to additional machining such as cutting. Further, to attach the bearing to the holding portion, a process for press fitting the bearing into the holding portion is required. This increases the manufacturing costs.
Recently, in accordance with the increased number of functions of vehicles, there is a demand for small motors. However, the end plate disclosed in the above document has the holding portion and the brush holder on opposite sides. That is, the bearing attached to the holding portion is located at one side of the end plate, while a commutator that contacts brushes attached to the brush holder is located at the other side of the end plate. In other words, the end plate is located between the bearing and the commutator with respect to the axial direction of the motor. This increases the size of the motor in the axial direction.